This invention relates to inflatable emergency evacuation slides used primarily on aircraft, and particularly to tie-back devices used in conjunction with these slides.
In the case of crash landings or other aircraft emergencies away from an airport terminal building, it is desirable to evacuate passengers or cargo as quickly as possible. Emergency evacuation slides have been provided on most aircraft for this purpose. Presently, the most common type of evacuation slide used is an inflatable ramp which is stored in its deflated condition. In emergencies, the deflated slide is extended from the aircraft and then inflated. When the slide is extended from the aircraft, it hangs in a relatively limp position. In this position it is highly vulnerable to wind deflection which occurs when a cross wind blows toward the evacuation exit. In such a case, the limp slide may be blown underneath the aircraft, thus making it completely useless when inflated. For further discussion of this problem, see U.S. Pat. No. 3,018,867. To eliminate the problem of wind deflection, devices have been used to restrain the full extension of the slide until it is almost fully inflated. In many such devices, the lower end of the slide is secured to the upper end until a suitable inflation pressure is attained. Upon release of the lower end of the slide, the inflation pressure forces the lower end to first swing outward from the aircraft, and then downward to the ground. Further discussion of the mechanics of this operation can be found in U.S. Pat. No. 3,391,771.
Preferably, the tie-back device used to secure the lower end of the slide is self-releasing when full extension of the slide is advantageous. A self-releasing restraint eliminates human error due to panic or lack of skill.
It is imperative that the restrain be released at a precise inflation pressure. Deviation from this pressure can render the slide useless. Release of an underinflated slide may cause wind deflection problems heretofore discussed. On the other hand, undue delay in fully extending the slide can be disastrous in a situation where time is of the essence. A restraint device which is set to release at an inflation pressure that will never be attained will also render the slide useless.
Hook and pile fasteners as in U.S. Pat. Nos. 3,606,939 and 3,669,217 are one of the many types of releasable restraints which have been proposed. Other proposals have included types of frictionally engaging components, as in U.S. Pat. Nos. 3,391,771 and 3,463,266.
Problems can arise regarding the dependability of the previously known types of releasable restraint devices. As was previously noted, release at a precise inflation pressure is necessary. General weather conditions, such as temperature, humidity and dampness can alter the predetermined release inflation pressure of hook and pile type fasteners. Weather and dampness can also have a detrimental effect on a friction type release device. Expansion and contraction of the friction materials can cause a change in the coefficients of friction of the engaging surfaces. This can cause a critical change in release inflation pressure. Corrosion due to exposure to the atmosphere can also affect the coefficients of friction of some friction type devices.
Many of the previously proposed devices are designed for reuse. Reuse ultimately causes wear which can change the release inflation pressure. Problems of incorrect release inflation pressure can arise when the device is being prepared for reuse by someone not skilled to do so. Furthermore most such devices are not tamperproof.
After deployment of the folded slide, most prior release devices have no protection from outside forces which can affect the release inflation pressure. For example, a wind blowing against the slide can cause the slide to twist. This can result in a twisting force being applied to the release device. Most devices cannot discriminate between forces from the inflation pressure and other forces. Thus, even though a particular device may release precisely upon application of a predetermined load, the load may be applied by forces that are irrelevant to inflation pressure.